The perovskite phase of lead magnesium niobate, Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 (PMN) is of interest for use in thin film capacitors and micro-electromechanical systems due to the very high dielectric constant and the electromechanical properties of PMN. The perovskite phase of PMN is very disordered and considered a classical relaxor ferroelectric. A relaxor ferroelectric can be distinguished from normal ferroelectric material by several properties. First, it has a broad Curie maximum point. The Curie point is the temperature at which ferroelectric material (material in which electric domains tend to be aligned parallel to one another) becomes paraelectric. For PMN, this broad Curie point is reportedly due to lattice and cation disorders which result in short range order, coupled with chemical inhomogeneous micro-regions. Other characteristics include a diffuse phase transition and a low-frequency dispersion of the dielectric constant. Single crystals of PMN have been shown to have a maximum dielectric constant of about 20,000 at 1 kHz; however, thin film dielectric permitivities are estimated to be around 1250 at room temperature. The electrical differences have been defined by the presence of a pyrochlore phase formed during the initial stages of conversion from metal alkoxides to the ceramic form.
Sol-gel-derived thin films are favored for production of PMN films due to the flexibility in the characteristics of solution precursors, the variety of deposition methodologies, and the reduction of the sintering temperatures. The standard solution approach to generating PMN thin films typically involves either using commercially available precursors and dissolving them in 2-methoxyethanol, which acts as both a solvent and a chemical modifier, or synthesizing large metallorganic "soap-derivative" (neo-decanoate) compounds using organic solvents such as xylenes. For the former method, water is generated as a by-product and further uncontrolled modifications occur. For the latter, identification of intermediates and higher organic pyrolysis temperatures are required due to the increased hydrocarbon content present.
Ravindranathan et al. ("Solution-Sol-Gel Processing of Lead Magnesium Niobate Thin Films," Ferroelectric Letters, Vol. 12, 1990, 29-34) teach a methoxyethanol approach to generating PMN thin films. In that method, commercially available acetates and alkoxides are heated in the presence of methoxyethanol to convert them to the methoxyethoxide derivatives. Ravindranathan's alcohol (methoxyethanol) necessarily serves both as solvent and modifier of precursor material.
In U.S. Pat. No. 4,636,248, issued to Ogata et al. on Jan. 13, 1987, a method is taught for precipitation of PMN precursor powders using metal alkoxides and water in alcohol solution. The alkoxides are mixed together and then hydrolized for 3 hours at elevated temperature to directly form the PMN precursor powders. An improvement would be to prepare a precursor solution from which either powders or thin films could be prepared (see Boyle, T. J., Dimos, D. B., and Moore, G. J., Ceram. Trans., First Internat. Symp. Adv. Synthesis Processing, in press). A further improvement would be to eliminate the hydrolization processing step so that synthesis could be performed without the 3-hr refluxing at elevated temperature.
Swartz et al, (U.S. Pat. No. 5,198,269, issued on Mar. 30, 1993) teach the basic physical process of deposition and heat treatment of metal alkoxide and acetate sol-gel coatings, a method commonly used to make thin films. For example, Swartz et al. disclose the benefit of insensitivity of the first deposition to a substrate, heat treatment to make the deposition isostructural to a second deposition, and further heat treatments--all physical considerations. Swartz et al. also teach the method of preparing thin film ferroelectric material precursors using methoxyethanol by a method similar to that described by Ravindranathan et al. (1990).